This invention relates generally to gas turbine engines and more particularly to exhaust duct liner attachment systems and methods. In gas turbine engines, it is necessary to protect exhaust ducts with an insulating shield in order to prevent heated core gases from damaging the exhaust ducts. Typically, exhaust ducts are made from titanium-based alloys and have temperature limits of approximately 300° F. (˜148.9° C.). Exhaust gases, however, reach much higher temperatures. It is, therefore, necessary to line exhaust ducts with a material that is capable of withstanding the peak temperatures of the core gases and that prevents the exhaust duct from reaching its temperature limitations. Exhaust duct liners are typically made from nickel-based alloys, which have temperature limits of approximately 700° F. (˜371.1° C.). In order to alleviate some of the heat from the exhaust gases imparted to the liner, cooling air is passed between the exhaust duct and liner. Thus, the exhaust duct and liner are subjected to different pressure and temperature gradients, which results in differing deflection and expansion of each body.
The differing deflections and expansions of the exhaust duct and liner are exacerbated by particular aircraft requirements. For military aircraft, it is sometimes desirable to have thrust vectoring capabilities or low radar signature profiles. Accordingly, the exhaust duct and liner must be tailored to meet these requirements. For example, thrust vectoring can be used for short take-off, vertical landing (STOVL) operations, which requires repositioning of the exhaust duct and nozzle. Additionally, low radar signature profiles require exhaust ducts to have streamlined shapes, which often require complex profiles that vary along the length of the duct.
In order to maintain the desired temperature and pressure profile along the exhaust duct and liner, it is necessary to maintain proper spacing between the exhaust duct and liner. The differing pressures, temperatures and functional requirements of the exhaust duct, however, produce three-dimensional forces between the duct and liner, which tend to shift the liner out of alignment. There is, therefore, a need for an exhaust duct liner suspension system that maintains proper spacing between an exhaust duct and a duct liner, while also permitting the liner to shift in other directions to accommodate, among other things, thermal growth.